1. Field of the Invention
The present invention relates to a method of peeling off a peeled off layer, particularly, relates to a method of peeling off a peeled off layer containing a variety of elements. In addition, the present invention relates to a semiconductor device having a circuit consisted of a thin film transistor (hereinafter, referred to as TFT) in which the peeled off layer peeled off has been pasted and transferred on a base member and a method of manufacturing the semiconductor device. For example, the present invention relates to an electro-optic device which is represented by a liquid crystal module, a light emitting device which is represented by an EL module and an electronic equipment on which such a device is mounted as a part.
It should be noted that in the present specification, the term “semiconductor device” indicates a device in general capable of functioning by utilizing the semiconductor characteristics, and an electro-optic device, a light emitting device, a semiconductor circuit and an electronic equipment are all semiconductor device.
2. Related Art
In recent years, a technology constituting a thin film transistor (TFT) using a semiconductor thin film (in the range from about a few to a few hundreds nm in thickness) formed on the substrate having an insulating surface has drawn the attention. A thin film transistor is widely applied to electronic devices such as an IC, an electro-optic device or the like, and particularly, there is an urgent need to be developed as a switching element for an image display device.
Although as for applications utilizing such an image display device, a variety of applications are expected, particularly, its utilization for portable apparatuses has drawn the attention. At present, although many glass substrates and quartz substrates are utilized, there are defaults of being easily cracked and heavy. Moreover, the glass substrates and quartz substrates are difficult to be made larger on the basis of mass-production, and these are not suitable for that. Therefore, the attempt that a TFT element is formed on a substrate having flexibility, representatively, on a flexible plastic film has been performed.
However, since the heat resistance of a plastic film is low, it cannot help lowering the highest temperature of the process. As a result, at present, a TFT is formed which has not so excellent electric characteristics compared with those formed on the glass substrates. Therefore, a liquid crystal display device and light emitting element having a high performance by utilizing a plastic film have not been realized yet.
Moreover, a method of peeling off a peeled off layer existing on the substrate via an isolated layer from the foregoing substrate has been already proposed. For example, technologies described in Japanese Unexamined Patent Publication No. H10-125929 gazette and Japanese Unexamined Patent Publication No. H10-125931 gazette are technologies that an isolated layer consisted of an amorphous silicon (or polysilicon) is provided, a laser beam is irradiated by transmitting the substrate and makes hydrogen contained in the amorphous silicon released, thereby occurring a space-gap and separating the substrate. In addition, there also has been the description in Japanese Unexamined Patent Publication No. H10-125930 gazette that by utilizing this technology, a liquid crystal display device is completed by pasting a peeled off layer (in the gazette, referred to as transferred layer) on a plastic film.
However, in the above-described method, it is essential to use a substrate having a high translucency, and further, for the purpose of conferring a sufficient energy for releasing hydrogen contained in the amorphous silicon, the irradiation of a comparatively large laser beam is necessary, and consequently a problem that the peeled off layer is damaged occurred. Moreover, in the above-described method, in the case where an element is prepared on an isolated layer, if a heat processing at a high temperature or the like is performed in the process of element preparation, hydrogen contained in the isolated layer is dispersed and reduced. In that case, even if the laser beam is irradiated on the isolated layer, there is a possibility that the peeling off is not sufficiently performed. Therefore, in order to maintain the amount of hydrogen contained in the isolated layer, a problem occurs that the processes after the isolated layer formation are limited. Moreover, in the above-described gazette, there has been also the description that in order to prevent the damage to the peeled off layer, a radiation shield layer or a reflection layer is provided. However, in this case, it is difficult to prepare a transmitting type liquid crystal display device. In addition, by the above-described method, it is difficult to peel off a peeled off layer having a large area.